Standardize ICCLIM / ETCCDI percentile precip indices

[tlogan2000]

Description

I recently participated in discussions with various groups who calculate ETCCDI (icclim) indices using various packages (e.g. R: climpact, climpact2, Python : icclim, xclim among other). The subject was wrt inconsistencies in index ids, long_name and output units for three percentile based precipitation indices. Consensus is to create 3 renamed versions of these indices (with standard output across all software). Old versions can be deprecated and eventually removed entirely

Index (long name)	Unit	Acronym
Total precipitation amount from days above percentile	mm	rXpSUM
Percentage of total precipitation amount from days above percentile	%	rXpPCT
Number of days when precipitation is above percentile	number of days	rXpDAYS

Deprecated ICCLIM indices:

• [ ] rXp
• [ ] rXpTOT

New indices notes:

• [ ] rXpDAYS == current rXp icclim indicator
• [ ] rXpPCT is similar to current rXpTOT but should return the % amount instead of a fraction between 0-1
• [ ] rXpSUM nothing similar is currently implemented in xclim

[tlogan2000]

@bzah can you double check this issue to make sure I did not leave anything out?

[bzah]

Looks good to me! I would just wait for a conclusion of the discussions before implementing these.

Maybe, one thing that was not discussed: xclim is capable of computing atmos.days_over_precip_thresh (standard rXpDAYS) and atmos.days_over_precip_doy_thresh (notice the "doy"). The later could lead to a new standard name I guess.